Isotopic exchange between alkanes and deuterium on rhodium/silica gel catalysts

Journal Article · Fri Jan 31 23:00:00 EST 1992 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1016/0021-9517(92)90241-9· OSTI ID:7202608

Takehara, D K; Butt, J B; Burwell, R L ^[1]

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1. Northwestern Univ., Evanston, IL (United States)

Isotropic exchange between deuterium and cyclopentane and between pentane and ethane on the Rh/SiO{sub 2} catalysts of the preceding paper has been investigated after several different pretreatments. Although a more restricted number of catalysts was examined, as with 2,2-dimethylbutane, increased percentage exposed (D{sub h}) appears to lead to increased turnover frequency (N{sub t}). After the standard pretreatment, H{sub 2}, 300 C; He, 450 C, the rates in alkane(g) {rightleftharpoons} alkane(ads) increase only slowly as D{sub h} increases, but the rates in monoadsorbed alkane {rightleftharpoons} diadsorbed alkane decline relatively rapidly. As with 2,2-dimethylbutane, the pretreatment H{sub 2}, 450 C leads to the largest values of N{sub t}. He, 450 C following H{sub 2}, 450 C removes surface hydrogen atoms and leads to reconstruction to a surface of much lower activity for exchange. Cyclopentane exchanges much faster than pentane on these catalysts. It appears that adsorption and desorption of cyclopentane involve single-step processes to and from diadsorbed cyclopentane + 2H*. Adsorption is faster than that with pentane because cyclopentane is essentially in the eclipsed conformation needed for this process. The rate of monoadsorbed {rightleftharpoons} diadsorbed cyclopentane is similarly augmented. Adsorbate-surface strain reduces the rate constant for adsorption of 2,2-dimethylbutane and increases rate of exchange of the hindered hydrocarbon vs that of the unhindered hydrocarbon will be larger than one would conclude merely from the relative rate constants of adsorption.

• OSTI ID: 7202608
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 133:2; ISSN 0021-9517; ISSN JCTLA
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020400 -- Petroleum-- Processing
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400202* -- Isotope Effects
Isotope Exchange
& Isotope Separation
ADSORBENTS
ADSORPTION
ALKANES
CATALYST SUPPORTS
CATALYSTS
CATALYTIC EFFECTS
CHEMICAL REACTIONS
CYCLOALKANES
DESORPTION
DEUTERATION
DEUTERIUM
ELEMENTS
ETHANE
HYDROCARBONS
HYDROGEN ISOTOPES
ISOTOPES
ISOTOPIC EXCHANGE
KINETICS
LIGHT NUCLEI
METALS
NUCLEI
ODD-ODD NUCLEI
ORGANIC COMPOUNDS
PENTANE
PLATINUM METALS
REACTION KINETICS
RHODIUM
SILICA GEL
SORPTION
STABLE ISOTOPES
SURFACE PROPERTIES
TRANSITION ELEMENTS